Method of extrusion and extrusion billet therefor



United States Patent Delaware No Drawing. Filed May 13, 1960, Ser. No. 28,844

8 Claims. (Cl. 148-115) The invention relates to an improved method of preparing an extrude of magnesium-base alloy and more particularly relates to an improvement in the method of preparing an extrude of precipitation-hardenable magnesiumbase alloy from particulated metal and to an improved extrusion billet.

'For the purposes of the specification and claims a magnesium-base alloy is defined as an alloy containing at least 75 percent by weight of magnesium.

Heretofore extrudes exhibiting good mechanical strength have been prepared by co-extruding particulated metals such as particulate magnesium-base alloy ZK60 admixed with particulate magnesium-aluminum alloy or aluminum. According to US. Patent 2,659,131 such an admixture of particulated metals is placed in the container of a preheated ram extrusion press and promptly die-expressed at relatively low speeds below about feet per minute, then heat treated after extrusion to bring about precipitation hardening. A serious drawback to this procedure is the necessity of employing low extrusion speeds and temperatures, the frequency of surface scoring of the extrude and the low ductility exhibited by the extrude.

It has now been found that, if the alloying constituents are heat treated while in intimate contact whereby a precipitation-hardened magnesium-base alloy is formed, prior to co-extrusion, substantial advantages are obtained.

The so obtained advantages are entirely unexpected because it was not known heretofore that precipitation hardened magnesium-base alloy could be readily worked after precipitation hardening. The more recent work on high strength alloys has been almost entirely centered on alloy systems which harden on being worked and are adversely affected when heat treated before extrusion. Therefore there has been a strong tendency to avoid heat treating extrusion 'billets before the extrusion thereof.

Appropriate alloying constituents for the present invention must meet the requirements that firstly, the final alloy contain at least 75 percent of magnesium, and secondly, that the other alloying constituents create problems in mutual alloying. Thus, the final alloy will contain at least 75 percent of magnesium and two or more additional alloying components that are mutually insoluble in solidified magnesium.

As used herein the term insoluble refers to solubility in solidified magnesium-base alloy.

This process applies to all magnesium systems which experience interference hardening, incompatibility, or compound formation. In the simplest form of the invention one of the mutually interfering alloying elements is employed as a component of a magnesium-base alloy and the other, desirably the more rapid diffusing of the two, is used in unalloyed form. For example, thorium may be used as a magnesium-base thorium-containing alloy and aluminum may be alloyed therewith according to the method of the invention.

In other modifications of the invention one of the mutually interfering alloying elements is employed as a component of a magnesium-base alloy and two or more alloying components interferring therewith are employed either as physical mixtures, or as alloyed together. The mutually interferring elements may also be brought together as components respectively of a magnesium-base alloy and a magnesium alloy if desired but the dilution of the interferring substances in the additional magnesium increases the heating time required for the diffusion process necessary for precipitation hardening and decreases the concentration of the solid-insoluble precipitates in the product of the invention.

Aluminum may be alloyed by the process of the invention with a magnesium-base alloy containing zirconium. Aluminum metal or magnesium alloys such as those containing from 20 to 30 percent by weight of aluminum may be employed as the source of aluminum. Magnesiumbase alloy containing zirconium may be alloyed with binary alloys or physical admixtures of aluminum and sili con, or, of aluminum and zinc. Other possible combinations are tabulated as follows:

MUTUALLY INSOLUBLE COMBINATIONS Component of magnesium base alloy: Other components 1 Zr Sn, Si, Zn. Mn Al, Si, Zr Th Al.

MM 2 Al. Li Al. Ca Al.

Employed singly or in combination or as a magnesium a iiiM=Misc11 metal.

The magnesium-base alloy employed may also contain non-interferring components which impart desired properties such as ductility, corrosion resistance or higher mechanical strength. As an example, magnesium-base alloy containing up to 0.8 percent zirconium and at least one of the following: up to 4 percent of zinc, up to 6 percent of silver, up to 1 percent of calcium, up to 4 percent of rare earth, up to 4 percent of thorium, up to 5 percent of lithium, may be admixed with aluminum or magnesiumaluminum alloy, and heat treated and extruded according to the invention.

All the metals are employed in particulated form. The magnesium-base alloy is conveniently used as atomized pellets such as those prepared according to US. Patent No. 2,676,359. The other metals are generally best used in finely divided form such as that passing about a No. 325 sieve (U.S. Sieve Series). Larger sizes tend to make complete precipitation hardening more difiicult, for example, by requiring a longer heat-treating period.

The proportions of each of the mutually interferring components employed in the process of the invention are not sharply critical. It is essential that a suliicient amount of each be present to cause formation of a solid insoluble precipiate throughout the magnesium-base alloy. When processed according to the present invention with l percent by weight of aluminum, a magnesium-base alloy containing as small a proportion of zirconium, such as 0.08 percent by weight, is found to have surprisingly increased strength properties, compared to a magnesium-base alloy containing either the aluminum or zirconium content alone. It is very desirable that the mutually insoluble component or components employed which are not a part of the initial magnesium-base alloy should be used in a small enough particle size and intimate enough dispersion that it will diffuse into the magnesium-base alloy in reasonable times at heat treating temperatures.

The magnesium-base alloy containing one of the mutually insoluble alloying components is brought into intimate contact with the additional insoluble component or components mainly in one of two ways.

The metals to be alloyed according to the invention are thoroughly blended and admixed, while in particulate form, as by tumbling the particles in a cylindrical container for 15 minutes or more. The thoroughly blended admixture is then placed in the preheated container of a die-extrusion press having a cover plate over the internal face of the die and the particles compacted under heat and pressure to a coherent mass, or extrusion billet. Thereafter the so-formed compact is ejected from the 4 periods tends to result in grain growth of the magnesium and agglomeration of the solid insoluble material whereby maximum strength is not achieved.

The extrusion billet may be machined to a smaller size,

press. Typically a compact is formed at 500 to 800 F. 5 if necessary, to permit easy insertion into the extrusion under a pressure of about 50 tons per square inch. container. As a modification of the compacting process of form- The heat treated metal, whether in the form of an ex- 1ng an extrusion b1llet the admixture may also be pretrusion billet or particulate metal, is then extruded at extruded at low reduct1on ratios such as 5 to 1, and at temperatures and reduction ratios well understood in the speeds of Z feet per minute or less and desi ably With magnesium metal art. Extrusion speeds, however, may a 10W ntalner temp ratur t avoid h shorting As he radically increased from about 1 or 2 feet per minute, an example, pre-extrusron may be carried out at 600 to heretofore used in the extrusion of such particulate ad- 700 F. with a container temperature of 600 F. and at mixtures, to speeds as high as 100 feet per minute. a speed of about 1 foot per minute. If desired, the extrusion billet formed in the process In another manner hnnglhg the {materials 111th lhtlof the invention may be placed in a close-fitting sleeve mate Contact the magnesmm-base alloy 1n solid particulate formed of either a conventional magnesium-base alloy or form y be f pp 111th, 0f p y Wlth, the other an aluminum-base alloy and transformed into rolled form metal or alloy 1n molten form, or gas plated or vacuum by passing it repeatedly, while at an elevated temperarnetalhzed or peen plated whereby a thin film of the other ture, between the rolls of a mill. The extrusion billet metal or alloy is deposited on substantially each particle may also be worked in other ways such as by forging of the magnesium-base alloy. An advantage of the platit i a manna n understood i h art, ing process is that the plated particles can be heat treated in particulated form if desired, and thereafter extruded Examples into final form thus avoiding a compacting or pre-extrusion step, 5 To 1llustrate the improved process of the invention The so-prepared compact or pro-extrusion, or the plated Various pelletized magnesium-has? alloys Containing particles described above, are then heat-treated for an Conlum and g Partlcle 8126 f ut 20 t 140 extended period to cause diffusion of the mutually inmesh (U. S. Sieve Senes) were thoroughly admixed with soluble alloying components whreby they meet and form fine alum num powder passing a 325 mesh sieve (U.S. solid insoluble particles, generally as intermetallic com- S16v6 The mlXtllreS W r a h mpacted into pounds, Heat treating the tal t 700 t 900 F, f extruslon billets at a temperature of about 650 F. and periods of 12 to 48 hours is generally adequate f th under a pressure of about 50 tons per square inch. The purposes of the invention, though shorter times may be extrusion billets Were each heat treated for 16 hours at used for mixtures formed from extremely fine particulate atemperature range of 750 to 0 F- Th s reat d material. The most advantageous temperatures and blllets were then scalped to reduce their dimensions slightly times vary somewhat with the magnesium alloy system so they would fit into the 3 inch diameter container of used and with the diliusion rates and particle sizes of a am t u n p e The b l ere a h expressed interfering alloying components. The heat-treating conthrough a die-opening by inch. The container ditions should be drastic enough to cause sufficient difmperat re was 6 0 F. and the strip was extruded at fusion into the magnesium-base alloy of any mutually a temperature of 650 F. Extrusion rates are shown in insoluble components originally external thereto that unthe a le. T e mechanical properties of the so-treated desired compounds, such as brittle magnesium al in extrudes were determined experimentally. The test results intermetallic compound, are dissociated whereby the final and th mposltl ns used are listed in Table I. One of extrude does not hot short and also whereby sufiicient the extllldes Was given a stahdal'd ASTM heat treatmhht, solid insoluble material is formed to significantly increase Which consisted of heating the eXtfllde for 24 hours the properties of the extrude. at 300 F. The properties of the so-treated extrude are On the other hand, heat treating for overly extended listed as Run No. 18.

TABLE I Composition of Composition of Mg-base alloy, Physical properties, 1000's p.s.i.

mixture, weight percent Extrusion Run N0. Weight percent speed, ft./ Percent E Al minute Zn Zr TYS CYS TS 0.25 1 0. 24 4 40 29 47 0. 25 1 0. 24 100 4 40 26 47 0.5 1 0. 24 100 5 41 31 4s 1 1 0. 24 50 4 41 36 4s 1 1 0. 24 100 6 42 33 4s 2 1 0. 24 100 9 41 40 4s 2 1 s 0. 24 100 12 41 40 48 3.6 1 0.24 50 s 45 42 51 3.6 1 0.24 100 8 44 43 51 4.4 1 0.24 90 10 47 44 53 6.2 1 0. 24 40 s 48 46 54 1 1 0.05 100 11 25 14 36 1 1 0.08 100 4 41 22 46 1 1 0. 32 100 10 41 39 4s 1 1 0. 64 50 6 4s 48 1 1 0.64 100 8 44 45 51 2 4.3 0. 64 40 4 50 51 56 2 4. 3 0. 64 T5 40 6 52 54 40 2 0.57 100 6 43 45 54 1 0. 24 50 9 29 15 a7 1 0. 24 100 10 27 13 36 0.6 100 11 23 11 34 1 Balance magnesium. 2 Balance magnesium-base alloy. Ts Ultimate tensile strength. 1.3 percent A1, 0.3 percent Mn (AZ1 1). T5:Standard ASTM heat treatment that was used after Percent E Percent elongation in 2 inches. die-expression of extrude. TYSzTensile yield strength. SzSieved, only particles passing number sieve were CYS Compression yield strength.

used.

For purposes of comparison extrudes containing zinc and zirconium but not aluminum, and, aluminum and zinc but not zirconium were prepared and the properties were were determined. The properties are listed in Table I. Also listed for comparison are the properties of an extrude formed by co-extruding magnesium-zirconium alloy with aluminum metal by a process not according to the method of the invention.

In a second series of experiments atomized magnesiumbase zirconium alloy, containing one or more additional alloying components was thoroughly admixed with fine particulate aluminum. The so-preparcd admixtures were compacted, heat-treated, scalped and extruded in the same manner as the admixtures tested in the first series of experiments. The compositions used, the extrusion speeds and the physical properties of the resulting extrudes are listed in Table II.

In a third series of experiments still an additional embodiment of the invention was carried out. Pellets of magnesium-base alloy containing zirconium were admixed with pellets of magnesium-aluminum alloy and the composition was compacted, heat-treated, scalped and extruded in the manner described in the first series of experiments. The physical properties of the resulting exexperiment pellets of magnesium-base alloy were admixed with aluminum pellets. The admixture was then tumbled in a cylindrical container to peen plate the pellets with aluminum. Both of the above compositions were compacted, heat-treated, scalped and extruded in the manner described in the first series of experiments. The physical properties of these extrudes were determined and are also listed in Table III.

Among the advantages of the invention are the sizeable increase in mechanical strength, ductility and permissible extrusion speed, as well as the freedom from hot shorts and surface imperfections in the extruded material produced according to the method of the invention.

I claim:

1. The improved process of forming a wrought article of magnesium-base alloy which comprises: preparing an intimate admixture consisting essentially of (1) particulate magnesium-base alloy containing at least one first alloying component and (2) at least one additional alloying component in finely divided form which is mutually solidinsoluble with said first alloying component in a magnesium-base alloy system, heat treating the said intimate admixture whereby precipitation hardening takes place, and working the so-heat treated intimate admixture.

trudes are determined and are listed in Table III. 2. In the process of forming a wrought article of mag- TABLE II Composition of Mg- Composition base Alloy, weight Other com- Extrusion Physical properties, l000s psi. Run No. of mixture, percent ponent(s) Weight speed, ieet/ Percent E weight metal percent minute percent Al Zr Zn TYS CYS TS 2 0. 6 2 100 4. 5 48 46 54 2 0. 6 1 2 46 44 52 2 O. 6 3 100 6 44 49 56 2 O. 6 2 100 8 46 54 2 0.6 g 100 10 49 48 55 2 0.6 g 70 6 46 48 53 1 0.42 3. 1 20 6 46 48 53 1 0. 42 3. 1 T5 20 4 47 51 55 1 0. 36 5. 6 15 4 48 52 2 0. 48 2. 8 100 3 49 49 53 2 0. 47 5. 5 7 49 52 56 1 0. 84 3. 3 5O 9 47 52 57 2 0.84 3. 3 30 8 49 56 58 2 0.84 3. 3 T5 30 4 50 59 1 B alance magnesiulmbase alloy. 2 Balance magnesium. Di=Mixture containing neodymium, praesodymium and small amounts of other rare earth metals.

TABLE III Composition of Mg- Aluminum source base alloy used, Extrusion Physical properties, lOOOs p.s.i. Run weight percent speed, No. feet/ Percent E minute Metal or Weight Particle Mesh Zn Zr TYS CYS TS alloy percent 1 form size a 34 Mg 4 Al 25 20 1 0. 24 100 5 39 30 46 35 Mg 10 Al. 10 20 1 0.24 100 6 32 17 39 3e Mg 10 AL 10 1 0. 24 5 39 2s 46 37 Mg 15 Al. 7 70 1 0. 24 100 5 32 16 41 3s Mg 33 Al 3 20 1 0. 24 100 2 25 16 31 39-- Mg 33 AL--- 3 70 1 0. 24 50 4 34 25 42 40-- Mg 33 Al 3 70 1 0. 24 100 2 32 24 39 41 A1 1 325 1 a 0. 5 100 4 42 35 50 2 Al 2.6 Atomized 325 1 b 0. 24 100 5 as 29 45 pellets.

1 Balance of the mixture magesium-base alloy.

2 Balance magnesium.

Chips machined from ingot; dimensions averaged about 0.020 x ,5 x inch.

In an additional experiment aluminum flake passing a 325 mesh sieve was admixed with chips of magnesiumbase alloy machined from an ingot. In still an additional Magnesium-base alloy mixed with the A1 pellets and tumbled in cylindrical container to peen plate the pellets with Al.

0 Number of sieve passed.

nesiurn-base alloy from particulate metal, the improved sequence of steps which comprises: compacting a thoroughly blended admixture consisting essentially of (1) particulate magnesium-base alloy containing at least one first alloying component and (2) at least one additional alloying component in finely divided form which is mutually solid-insoluble with each said first alloying component in a magnesium-base alloy system; heat treating the intimate admixture whereby precipitation hardening takes place in the admixture; and subjecting the heat treated admixture to a wrought operation.

3. In the process of forming a Wrought article of magnesium-base alloy from particulate metal, the improved sequence of steps which comprises: preparing an intimate admixture consisting essentially of (1) particulate magnesium-base alloy containing at least one first alloying component and (2) at least one additional alloying component in finely divided form which is mutually solid-insoluble with each said first alloying component in a magnesium-base alloy system; heat treating the intimate admixture whereby precipitation hardening takes place in the admixture; and extruding the heat treated admixture.

4. In the process of forming a wrought article of magnesium-base alloy from particulate metal, the improved sequence of steps which comprises: preparing an intimate admixture consisting essentially of (1) particulate magnesium-base alloy containing at least one first alloying component and (2) at least one additional alloying component in finely divided form which is mutually solid-insoluble with each said first alloying component in a magnesium-base alloy system, said additional alloying component being in a form selected from the group consisting of (a) the substantially pure metal, (b) mixtures and alloys of metals each mutually insoluble with said first alloying component, and (c) magneisum alloys containing at least one said additional alloying component; heat treating the intimate admixture whereby precipitation hardening takes place; and extruding the heat treated admixture.

5. In the process of forming a wrought article of magnesium-base alloy from particulate metal, the improved sequence of steps which comprises: coating (1) particulate magneisum-base alloy containing at least one first alloying component with (2) at least one additonal alloying component which is mutually solid-insoluble with each said first alloying component in a magnesium-base alloy system; heat treating the coated particles of said magnesium-base alloy whereby precipitation hardening takes place; and extruding the heat treated particles.

6. In the process of forming a wrought article of magnesium-base alloy from particulate metal, the improved sequence of steps which comprises: compacting an intimate admixture consisting essentially of 1) particulate magnesiuIn-base alloy containing at least one first alloying component and (2) at least one additional alloying component in finely divided form which is mutually solid-in soluble with each said first alloying component in a magnesium-base alloy system, under sufiicient heat and pressure to form a coherent compact; heat treating the compact whereby precipitation hardening takes place therein; and extruding the heat treated compact.

7. In the process of forming a wrought article of magnesium-base alloy from particulate metal, the improved sequence of ste s which comprises: pre-extruding an intimate admixture consisting essentially of (1) particulate magnesium-base alloy containing at least one first alloying component and (2) at least one additional alloying component in finely divided form which is mutually solidinsoluble in a magnesium-base alloy system; heat treating the pre-extruded admixture whereby precipitation hardening takes place therein; and extruding the preextruded and heat treated admixture.

S. In the process of forming a wrought article of magnesium-base alloy from particulate metal, the improved sequence of steps which comprises: preparing a thoroughly blended admixture consisting essentially of 1) particulate magnesium-base alloy containing zirconium as an alloying component and (2) aluminum in finely divided form; subjecting the intimate admixture to heat and pressure whereby sufiicient particles of the admixture are Welded together to form a coherent mass; heat treating the coherent mass whereby precipitation hardening takes place; and extruding the so-heat treated admixture.

References Cited by the Examiner UNITED STATES PATENTS 321,658 7/1885 Sweet 29--187 1,648,678 11/1927 Ehlers 29192 2,249,353 7/1941 Fritzlen 14812.7 2,358,667 9/1944 Stern 20710.2 2,391,752 12/1945 Stern 207-1().2 2,659,131 11/1953 Leontis et a1. 148-12.7 3,024,107 3/1962 Foerster et a1. 14811.5

OTHER REFERENCES Busk and Leontis: The Extrusion of Powdered Magnesium Alloys, Trans. AIME, vol. 188 (1950), pp. 297- 306.

DAVID L. RECK, Primary Examiner.

WILLIAM M. DYER, JR., Examiner. 

1. THE IMPROVED PROCESS OF FORMING A WROUGHT ARTICLE OF MAGNESIUM-BASE ALLOY WHICH COMPRISES: PREPARING AN INTIMATE ADMIXTURE CONSISTING ESSENTIALLY OF (1) PARTICULATE MAGNESIUM-BASE ALLOY CONTAINING AT LEAST ONE FIRST ALLOYING COMPONENT AND (2) AT LEAST ONE ADDITIONAL ALLOYING COMPONENT IN FINELY DIVIDED FORM WHICH IS MUTUALLY SOLIDINSOLUBLE WITH SAID FIRST ALLOYING COMPONENT IN A MAGNESIUM-BASE ALLOY SYSTEM, HEAT TREATING THE SAID INTIMATE ADMIXTURE WHEREBY PRECIPATION HARDENING TAKES PLACE, AND AND WORKING THE SO-HEAT TREATED INDIATE ADMIXTURE. 